Stream流flatMap的使用

 用流白摆脱双层for循环，实现setRecord。

当然转换流还可以生成新的类型的流对象。

package Test;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

/**
 * @description:
 * @author: yq
 * @time: 2022/3/13 8:17
 */
public class StreamTest {

    private static List<Developer> developers;
    private static List<Record> records;

    static {
        Developer developer1 = new Developer("11", "111", "ww", 10);
        Developer developer2 = new Developer("22", "222", "qq", 20);
        Developer developer3 = new Developer("33", "333", "ee", 30);
        Developer developer4 = new Developer("44", "444", "rr", 40);

        Record record1 = new Record("1", "ww", "原因");
        Record record2 = new Record("2", "qq", "原因");
        Record record3 = new Record("3", "rr", "原因");
        Record record4 = new Record("4", "ee", "原因");

        developers = new ArrayList<>();
        developers.add(developer1);
        developers.add(developer2);
        developers.add(developer3);
        developers.add(developer4);

        records = new ArrayList<>();
        records.add(record1);
        records.add(record2);
        records.add(record3);
        records.add(record4);
    }


    public static void main(String[] args) {

        List<Developer> developerList = developers.stream().filter(ele -> ele.getAge() >= 20).flatMap(ele -> {
            return records.stream()
                    .filter(record -> ele.getUserId().equals(record.getRelationId()))
                    .map(record -> {
                        ele.setRecord(record);
                        return ele;
                    });
        }).collect(Collectors.toList());


        developerList.forEach(System.out::println);

    }

    static class Developer {
        private String id;
        private String name;
        private String userId;
        private Record record;
        private Integer age;

        public Developer() {
        }

        public Developer(String id, String name, String userId, Integer age) {
            this.id = id;
            this.name = name;
            this.userId = userId;
            this.age = age;
        }

        @Override
        public String toString() {
            return "Developer{" +
                    "id='" + id + '\'' +
                    ", name='" + name + '\'' +
                    ", userId='" + userId + '\'' +
                    ", record=" + record +
                    ", age=" + age +
                    '}';
        }

        public Integer getAge() {
            return age;
        }

        public void setAge(Integer age) {
            this.age = age;
        }

        public Record getRecord() {
            return record;
        }

        public void setRecord(Record record) {
            this.record = record;
        }

        public String getId() {
            return id;
        }

        public void setId(String id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getUserId() {
            return userId;
        }

        public void setUserId(String userId) {
            this.userId = userId;
        }
    }

    static class Record {
        private String id;
        private String relationId;
        private String reason;

        public Record(String id, String relationId, String reason) {
            this.id = id;
            this.relationId = relationId;
            this.reason = reason;
        }

        public Record() {
        }

        @Override
        public String toString() {
            return "Record{" +
                    "id='" + id + '\'' +
                    ", relationId='" + relationId + '\'' +
                    ", reason='" + reason + '\'' +
                    '}';
        }

        public String getId() {
            return id;
        }

        public void setId(String id) {
            this.id = id;
        }

        public String getRelationId() {
            return relationId;
        }

        public void setRelationId(String relationId) {
            this.relationId = relationId;
        }

        public String getReason() {
            return reason;
        }

        public void setReason(String reason) {
            this.reason = reason;
        }
    }
}